1. Field of the Invention
The present invention relates to an accuracy analyzing apparatus for a machine tool in which a table and a main spindle are relatively moved in three orthogonal axial directions of a first axis that elongates along the axis of the main spindle, and second and third axes that are perpendicular to each other, and also to the first axis. Such an accuracy analyzing apparatus is used for analyzing the perpendicularity of the axis of the main spindle with respect to a plane defined by the second and third axes.
2. Description of the Prior Art
The perpendicularity of the axis of the main spindle directly affects the machining accuracy. Before shipment from the manufacturer of the machine tool to the user, therefore, the perpendicularity is usually checked and adjusted so as to attain a predetermined reference value.
As an apparatus for checking the perpendicularity, the inventor of the present invention has proposed an accuracy analyzing apparatus shown in FIG. 7. As shown in FIG. 7, the accuracy analyzing apparatus 100 comprises: a laser oscillator 101 attached to a main spindle 115 of a machine tool 110; a CCD camera 102 which is placed and fixed onto a table 113 so as to be opposed to the laser oscillator 101; an analyzer 103 which analyzes the accuracy of the machine tool 110 on the basis of an image picked up by the CCD camera 102; and an outputting device (not shown) which displays or prints out a result of the analysis performed by the analyzer 103.
For example, the machine tool 110 has the structure configured by: a bed 111; a column 112 which is fixed onto the bed 111; a table 113 which is placed on the bed 111, and which is movable in a horizontal plane and two orthogonal axial directions (X- and Y-axis directions); a spindle head 114 which is supported by the column 112 so as to be movable in the vertical direction (Z-axis direction), and which supports the main spindle 115 so that the main spindle 115 is rotatable about an axis thereof; a first feed mechanism (not shown) which moves the spindle head 114 in the Z-axis direction; a second feed mechanism (not shown) which moves the table 113 in the Y-axis direction; a third feed mechanism (not shown) which moves the table 113 in the X-axis direction; and an NC apparatus 116 which controls the operations of the first feed mechanism, the second feed mechanism, and the third feed mechanism, and the like.
The laser oscillator 101 emits laser beam, and as described above is attached to the main spindle 115 and set so that the light axis of the laser beam is coaxial with the axis of the main spindle 115. The CCD camera 102 comprises as imaging elements a plurality of photoelectric conversion elements which are two-dimensionally arranged in a multi-row, multi-column array. The CCD camera 102 digitizes voltage signals which are output from the photoelectric conversion elements in accordance with the amount of received light, converts the digitized signals into density level values, and outputs the values as two-dimensional density image data which are arranged in the same manner as the arrangement of the photoelectric conversion elements.
The analyzer 103 binarizes by a predetermined threshold the two-dimensional density image data which are output from the CCD camera 102, to extract an image corresponding to the laser beam, and analyzes the extracted binary image to analyze the accuracy of the machine tool 110.
For example, the axis of the main spindle 115 will be considered. In the case where the axis of the main spindle 115 is inclined with respect to the Z-axis as shown in FIG. 8, when the spindle head 114 is moved in the Z-axis direction by the first feed mechanism (not shown), a deviation is caused between the center position of the binary image which is extracted before the movement, and that of the binary image which is extracted after the movement. On the basis of the binary images which are obtained before and after the movement, for example, the analyzer 103 calculates the deviation amount d of the center position, and, based on the calculated deviation amount d and the movement distance m in the Z-axis direction, calculates the inclination angle of the axis of the main spindle 115 with respect to the Z-axis to analyze the perpendicularity of the axis of the main spindle 115 with respect to the horizontal plane (a plane defined by the X- and Y-axes).
The accuracy analyzing apparatus 100 can precisely analyze the accuracy of the machine tool 110 or the perpendicularity of the axis of the main spindle 115. In the accuracy analyzing apparatus 100, however, the accuracy analyzation requires the cumbersome work of operating the first feed mechanism (not shown) to move the spindle head 114 in the Z-axis direction, and hence is not always efficient. Accordingly, a need remains for an improved accuracy analyzing apparatus. Moreover, there is the possibility that the accuracy analyzing apparatus 100 is damaged by an erroneous operation during the movement of the spindle head 114.
The invention has been conducted in order to achieve the improvement. It is an object of the invention to provide an accuracy analyzing apparatus in which the perpendicularity of the axis of a main spindle can be efficiently analyzed by a simple operation.